Controllable digital solid state cluster thrusters for rocket propulsion and gas generation

ABSTRACT

A thruster stack assembly and method for manufacturing the same is provided. The thruster stack assembly includes a plurality of grain elements having a common core region (e.g., a channel or passageway), where each grain element comprises a volume of electrically ignitable propellant. The thruster stack assembly further includes electrodes associated with the plurality of grain elements, the electrodes adapted for selectively igniting the plurality of grain elements. In one example, one or more of the grain elements may be ignited and combusted without igniting or damaging adjacent grain elements of the stack. The core region serves to channel combustion gases and exhaust from the thruster stack. Multiple stacks may be assembled together to form three-dimensional thruster arrays.

RELATED APPLICATION

This application is related to and claims benefit of previously filedU.S. provisional patent application Ser. No. 60/637,018, filed Dec. 17,2004, and entitled “CONTROLLABLE DIGITAL SOLID STATE CLUSTER THRUSTERSFOR ROCKET PROPULSION AND GAS GENERATORS”; the entire content of whichis hereby incorporated by reference in its entirety as if fully setforth herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Certain aspects herein were made in part during work supported by aSmall Business Innovative Research contract from the United States ofthe Secretary of Defense; contract F04611-03-M-3-3-012: (ENHANCEMENT OFCOMBUSTION SURFACE CONDUCTIVITY OF THE ELECTRICALLY CONTROLLEDEXTINGUISHABLE SOLID PROPELLANT); and a Small Business InnovativeResearch contract from the United States Army, contract: W31P4Q04CR144(THROTTLED PROPULSION USING AN ELECTRICALLY CONTROLLED EXTINGUISHABLESOLID PROPELLANT DUAL-STAGE MOTOR). The government may have certainrights in the invention.

SECRECY ORDER

The present application incorporates by reference provisional patentapplication Ser. No. 60/637,018, currently under a secrecy order under37 CFR 5.2. Further, the present application incorporates by referenceU.S. patent application Ser. No. 10/136,786, entitled “ElectricallyControlled Propellant Composition and Method”, which may be or may havebeen under a secrecy order under 37 CFR 5.2.

BACKGROUND

1. Field

The present invention relates generally to solid state thrusters, and inone particular example to controllable digital solid state clusterthrusters for propulsion, igniters, electric matches, pyrotechnicdisplays, and/or gas generation that includes an electrically ignitablepropellant.

2. Description of Related Art

Digital propulsion systems, and in particular, arrays of microthrustersare known. Generally, a digital propulsion system includes atwo-dimensional array of individually addressable thrusters, which maybe selectively fired for purposes of propulsion or gas generation. Inone example, described generally in “Digital MicroPropulsion”, by Lewiset al., Sensors and Actuators A, Physical, 2000, 80(2) pp 143-154, andwhich is incorporated by reference, an array of microthrusters areformed, where each microthruster includes a micro-resistor, thrustchamber, and rupture diaphragm. A propellant is disposed in the thrustchamber and may be ignited by energizing (and thus heating) themicro-resistor to a sufficient temperature to ignite the propellant.When the propellant is ignited the pressure in the chamber rises untilthe diaphragm is ruptured, resulting in the ejection of material fromthe chamber. The ejection of material results in a thrust imparted tothe microthruster. Such microthrusters may be manufactured as dies orchips including an array of varying number and sized microthrusters.Further, the resisters may be selectively addressed to ignite and impartvarying amounts of thrust.

SUMMARY

In one aspect of the present invention a thruster stack is provided. Inone example, the thruster stack assembly includes a plurality of grainelements having a common core region (e.g., a channel or passageway),each grain element comprising a volume of electrically ignitablepropellant. The thruster stack assembly further includes electrodesassociated with the plurality of grain elements, the electrodes adaptedfor selectively igniting the plurality of grain elements. In oneexample, one or more of the grain elements may be ignited and combustedwithout igniting or damaging adjacent grain elements of the stack. Thecore region serves to channel combustion gasses and exhaust from thethruster stack.

In some examples, the thruster stack assembly may include an insulationlayer and/or electrodes disposed between two adjacent grain elements. Inother examples, adjacent grain elements may be disposed in directcontact with each other. The grain elements may include two coaxiallyaligned rings of electrically ignitable propellant, the center of therings defining a common core region. Additionally, a thruster stackassembly may include a plurality of stacked thrusters, each thrusterhaving a plurality of grain elements, thereby forming athree-dimensional array of addressable grain elements.

According to another aspect of the present invention, a method formanufacturing a thruster stack array is provided. In one example, themethod includes layering vertically at least two dies having chambersformed therein, wherein a first chamber from a first die and a secondchamber from a second die are aligned vertically, disposing two or moreelectrodes adjacent each cavity, affixing the at least two diestogether, and disposing electrically ignitable propellant within thefirst and second cavities.

The method may further including removing propellant from the first andsecond chambers to form a common core region associated with thepropellant in the first and second chambers. Each of the first andsecond chambers may thereby form separate grain elements that may beselectively ignited by the electrodes.

The present inventions and various aspects are better understood uponconsideration of the detailed description below in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B illustrate cross-sectional side and top views,respectively, of a first exemplary “core burner” structure including anelectrically ignitable propellant.

FIGS. 2A and 2B illustrate cross-sectional side and top views,respectively, of a second exemplary “core burner” structure including anelectrically ignitable propellant.

FIGS. 3A and 3B illustrate cross-sectional side and top views,respectively, of a third exemplary coaxial electrode structure includingan electrically ignitable propellant.

FIG. 4 illustrates an exemplary thruster structure including anelectrically ignitable propellant according to another example.

FIGS. 5A-5C illustrate an exemplary combustion process of a structureincluding an electrically ignitable propellant according to the exampleof FIG. 4.

FIG. 6 illustrates an exemplary configuration and method for forming athruster stack array of grain elements.

FIGS. 7A and 7B illustrate cross-sectional side and top views,respectively, of an exemplary cluster structure allowing individualcontrol of multiple fuel grain elements within multiple thruster/gasgenerators.

FIGS. 8A and 8B illustrate cross-sectional side and top views,respectively, of another exemplary cluster structure allowing individualcontrol of multiple fuel grain elements within multiple thruster/gasgenerators.

DETAILED DESCRIPTION

The following description is presented to enable a person of ordinaryskill in the art to make and use various aspects and examples of thepresent invention. Descriptions of specific materials, techniques, andapplications are provided only as examples. Various modifications to theexamples described herein will be readily apparent to those of ordinaryskill in the art, and the general principles defined herein may beapplied to other examples and applications without departing from thespirit and scope of the invention. Thus, the present invention is notintended to be limited to the examples described and shown, but is to beaccorded the scope consistent with the appended claims.

Methods and systems for controllable digital solid state clusterthrusters and gas generators are described. Exemplary systems andmethods may be used, for example, to ignite, throttle, extinguish, andre-start the combustion of high performance solid rocket propellants.Additionally, exemplary methods and systems may be used as gasgenerators in a variety of application. Various examples describedherein may be used in rockets, missiles, spacecraft, aircraft,sea-craft, and land vehicles for propulsion or as an on-demand gasgenerator. In one example, a solid state (i.e., no moving parts)hardware system is manufactured using either mechanical (drill, punch,cast, formed) and/or photographic/chemical etching and vapor deposition,such is used in printed circuit and/or wafer (integrated circuit)fabrication processes common in the semiconductor industry.

One exemplary propellant includes the use of solid/solid-solution rocketpropellants that are controlled by the application of electrical power,e.g., where ignition and/or combustion of the propellant is sustained bysupplying electrical power (referred to herein generally as“electrically ignitable propellant”). Such a propellant is described inU.S. patent application Ser. No. 10/136,786, entitled “ElectricallyControlled Propellant Composition and Method”, the entire content ofwhich is hereby incorporated by reference as if fully set forth herein.The use of an electrically ignitable propellant obviates the need forigniters (e.g., spark or other thermal igniters such as resistorelements or the like) to initiate propellant combustion. Accordingly, inexamples described herein, combustion of a specific volume of propellant(referred to herein as a “grain” or “grain element” of propellant) isinitiated and/or controlled by electrical power between electrodes andthrough the propellant.

Exemplary thrusters and gas generators described herein may be desirablebecause they are controllable and have no moving parts. Grain elementscan also be stacked into three-dimensional arrays, without the need toseparate or channel hot combustion gases away from adjacent unusedpropellant grains. Scaling of manufacturing methods spans from those ofthe semiconductor industry for microchips, such as photo etching andchemical vapor deposition, upwards to drill, stamped, or molded dieslayered together for larger devices. These manufacturing methods mayallow mass production of these devices at relatively low compared toconventional thruster devices.

FIGS. 1A and 1B illustrate cross-sectional side and top views,respectively, of a first exemplary “core burner” structure 100 includingan electrically ignitable propellant 102. In this example, structure 100includes a single grain element or volume of electrically ignitablepropellant 102 to be ignited and controlled by electrodes 101 a and 101b. In operation, washer-shaped electrodes 101 a and 101 b conductcurrent through the electrically ignitable propellant 102 causingelectrically controlled combustion. The application of voltage toelectrodes 101 a and 101 b may be controlled to combust a portion or allof the propellant 102. Further, structure 100 is generally configuredsuch that combustion initiates from the middle or core region 104 andproceeds radially outward. During combustion, exhaust gases and heat arechanneled via core region 104 to exit through an aperture or port 103.

In this example, washer shaped electrodes 101 a and 101 b are disposedaxially on opposite ends of a housing 108 containing propellant 102.Housing 108 may include a cylindrical insulating case for containingpropellant 102 and is closed by electrodes 101 a and 101 b disposed oneach end thereof. At least one of the electrodes 101 a and 101 bincludes an aperture or port 103 at an end of core region 104 whichallows for the escape of heat and gas from combustion of propellant 102.

Propellant 102 is disposed within housing 108 in an annuluscross-sectional shape, thereby defining central core region 104 disposedalong the axis of structure 100. Propellant 102 may be disposed withhousing 108 in any manner, for example, cast, poured, vacuum poured orthe like into housing 108 or other suitable packaging. Central coreregion 104 may be formed within propellant 102 by drilling or other postprocessing (e.g., etching, punching, or other material removalprocesses). Further, in this example, central core region 104 is alignedat least partially with an aperture in washer electrode 101 a (orotherwise formed in electrodes 101 a, 101 b, or housing 108) to assistin channeling gas and heat through port 103 and out of structure 100.

FIGS. 2A and 2B illustrate cross-sectional side and top views,respectively, of a second exemplary “core burner” structure 200including an electrically ignitable propellant 202. In this example,which is similar to structure 100, structure 200 includes flat, ribbonshaped electrodes 201 a and 201 b positioned lengthwise along structure200 (e.g., along the axis and extending radially from the center coreregion 204). In operation, with sufficient potential applied acrosselectrodes 201 a and 201 b, electrical current will pass betweenelectrodes 201 a and 201 b causing electrically controlled combustion ofpropellant 204. Combustion will begin along the central core region 204similar to that described above with reference to structure 100 of FIGS.1A and 1B.

FIG. 2A further illustrates electrical connectors 212 which may bedisposed on either or both sides of structure 200. Electrical connectors212 may include pins or leads for connecting electrodes 201 a and 201 bto a power source or die (neither of which are shown). Further shown areforward and aft closures or nozzles 220, positioned adjacent exhaustports 203, and which may be included on either or both axial ends ofstructure 200 and core region 204. Nozzles 220 may be used to controlcombustion or gas generation of structure 200 as will be understood bythose of ordinary skill in the art.

Electrodes 201 a and 201 b are shown positioned 180 degrees apart fromeach other. In other examples, however, electrodes 201 a and 201 b maybe positioned differently; further, multiple sets of electrodes may bedisposed within propellant 202, thereby creating multiple grainelements.

FIGS. 3A and 3B illustrate cross-sectional side and top views,respectively, of an exemplary coaxial electrode structure 300 includingan electrically ignitable propellant 302. In this example, electrodes301 a and 301 b are disposed coaxially with electrically ignitablepropellant 302 disposed therebetween. In particular, electrode 301 aincludes an outer ring shaped electrode and electrode 301 b includes arod or smaller ring shaped electrode disposed within electrode 301 a.

As previously described, propellant 302 is ignited with suitablepotential supplied across electrodes 301 a and 301 b. In this example,an exhaust port is positioned generally at the axial top and/or bottomaxial face of structure 300. In one example, a housing (not shown) maybe included to cover the bottom axial surface of structure 300 such thatas propellant 302 is ignited and combusted from the top axial surfaceand proceeds downward. Burn away insulation may be used on one or bothelectrodes 301 a and 301 b. Multiple structures may be grouped orclustered together using a common electrical ground to provideindividual combustion control with fewer wires. Such a cluster may bepotted in a suitable matrix forming a unified solid-state device.

FIGS. 4 and 5A-5C illustrate another exemplary electrode structure 400including an electrically ignitable propellant 402. In this example,electrodes 401 a and 401 b include flexible or ridged flat plates thatare manufactures as a layered structure and then rolled into acylindrical structure (as indicated generally in FIG. 4) or stacked flatinto a multi-layer structure. The exemplary method and structure maypreserve electrode spacing and enable larger amounts of propellant to beburned efficiently during use. For example, coaxial electrode structuressuch as illustrated in FIGS. 3A and 3B, include core and outerelectrodes that have different surface areas. The different surfaceareas of the electrodes may result in radial electrical current densityvariations that may cause combustion inefficiency during operation. Theuse of flat plate electrodes 401 a and 401 b (which are spiraled into afinal structure 400 shown in FIG. 4) may allow more uniform electricalcurrent density therebetween and more efficient combustion of thepropellant 402.

In one example, structure 400 includes electrodes 401 a and 401 b, aninsulation layers 405 disposed on electrodes 401 a and 401 b, and anelectrically ignitable propellant 402 therebetween. In one example,propellant 402 is disposed, e.g., cast or otherwise layered ontoinsulation layer 401 and/or electrodes 401 a and 401 b, at a thicknessof approximately 0.12 inches (of course, other propellant thicknessesare possible). The separation between electrodes 401 a and 401 b may bevaried for efficient combustion of propellant, such as HIPEP propellant(High Power Electric Propulsion propellant). HIPEP propellant isdescribed, for example, in AFRL-PR-ED-TR-2004-0076, “High PerformanceElectrically Controlled Solution Solid Propellant,” Arthur Katzakian andCharles Grix, Final Report, the entire content of which is incorporatedby reference herein. In one example, electrically ignitable propellant,such as HIPEP propellants, are generally flexible when cured. Further,the use of flexible foils or thin metal layers for electrodes 401 a and401 b allows for rolling thick films or layers of the electrodes 401 aand 401 b and propellant 402 into spiral shaped structures as shown inFIG. 4.

Additionally, the material of electrodes 401 a and 401 b, e.g., aluminumor other suitable material, may be consumed during combustion ofpropellant 402, thereby increasing the specific impulse of the thrusteror other device while still allowing multiple extinguishments. In oneexample, however, the material of the electrodes 401 a and 401 b maycause propellant 402 to self sustain combustion (i.e., the propellantwill not extinguish when power to electrodes 401 a and 401 b is ceased).Accordingly, the electrode metal, thickness, volume, etc., may beconfigured so as to be consumed during combustion, but not lead to selfsustaining combustion of propellant 402. In other examples, electrodes401 a and 401 b may include stainless steel or the like so as to not beconsumed by the combustion. Additionally, insulation layer 405, whichmay include Teflon or Phenolic coatings, may also be combusted withpropellant 402.

FIGS. 5A-5C illustrate an exemplary combustion process of a portion ofpropellant 402 of structure 400. As seen in FIG. 5A, insulation layers405 do not extend to the edge of the layered structure 400 such that aportion of propellant 402 contacts opposing electrodes 401 a and 401 b.Electrodes 401 a and 401 b may be energized to initiate combustion inthis region of structure 400. As the electrodes 401 a and 401 b continueto be energized, as shown in FIG. 5B, propellant 402 and insulationlayers 405 combust (heat and gas exiting to the right). The insulationlayer 405 burns away in front of the flame front, thereby sustaining acontact between electrodes 401 a and 401 b and propellant 402. The powersupplied to electrodes 401 a and 401 b may be stopped, as shown in FIG.5C, and combustion ceased. The insulation layer 405 burns away in frontof the flame front or combustion of propellant 402 such that whencombustion is ceased electrodes 401 a and 401 b are still in contactwith propellant 402 and may be reinitiated by providing power toelectrodes 401 a and 401 b.

According to another aspect described herein, multiple structures forigniting electrically ignitable propellant (e.g., structures 100, 200,300 or 400), may be combined into arrays of individually addressablegrain elements. For example, multiple grain elements or structuressimilar to those illustrated by structures 100, 200, 300, or 400 may becombined or stacked into a variety of thruster arrays suitable forvarious propulsion or gas generation devices.

FIG. 6 illustrates an exemplary configuration and method for forming athruster stack array 600, which may be used for propulsion and/or gasgeneration. The exemplary method results in a thruster stack assembly600 that allows for individual control of four fuel grain elementswithin each of three vertically aligned thrusters as shown incross-sectional and top views in FIGS. 7A and 7B, which are referencedin conjunction with FIG. 6. As will be appreciated by those of ordinaryskill in the art, the number of thrusters and vertically aligned grainelements are illustrative only, and any number of thrusters and/or grainelements are possible. Further, various examples of grain elementsdescribed herein, e.g., with reference to FIGS. 1-4, may be combinedinto a thruster stack array.

In this example, common electrode dies 610 and individual electrode dies611 are disposed (e.g., stacked or layered vertically) with insulatingpropellant chamber dies 614 a-614 d. Chamber dies 614 a-614 d includechambers 615, which will have propellant disposed therein. Chamber dies614 a-614 d, and in particular chambers 615, are aligned vertically.Electrode dies 610 and 611 are also aligned vertically with each otherand chamber dies 614 a-614 d. Additionally, a forward electrode 612 andan aft nozzle or gas exhaust connection 613 may be included with theassembly. The stack of electrode dies 610 and 611 and chamber dies 614a-614 d are laminated or otherwise affixed or housed together as asingle assembly.

Once the stack is laminated, suitable propellant is disposed withinchamber dies 614 a-614 d, and in particular, chambers 615. Thepropellant may be disposed within chambers 615 by any suitable method.For example, propellant may be poured, vacuum poured, cast, or otherwiseintroduced into chambers 615 of chamber dies 614 a-614 d. As shown, thepropellant chamber dies 614 a-614 d have individual openings forcontaining propellant having a larger radial surface than apertures inelectrode dies 601 a and 601 b such that when filled with propellantelectrode dies 601 a and 601 b are in contact with propellant therein(such that propellant 602 may be ignited).

The exemplary methods and structures described allow for multiplethruster units to be manufactured simultaneously, reducing costs whileproviding redundancy. The examples are generally scalable and allowseveral different size thrusters to be included in a single assembly.The grain elements may be in direct contact with one another orseparated by conductive electrodes or insulating layers as shown anddescribed. Further, the electrodes may include conductive materials suchas copper, aluminum, stainless steel, zirconium, gold, and the like.Insulator materials for the dies, casing, or to separate grains mayinclude rubber, phenolic, Teflon®, ceramic, and the like. The electrodegeometries may be configured to allow specific volumes or surfaces ofpropellant to be ignited individually and/or in combination to achievedesired thrust/gas generation control. Electrode geometry and/orconductive surface coatings can control propellant combustion eitherproceeding inward from surfaces or to instantaneously ignite specificvolumes. Electrode surfaces may be varied from smooth to porous meshchanging the surface area in contact with the propellant. Once thehardware assemblage/stack is formed, the propellant is added by castingwith or without vacuum depending on scale. Additionally, mandrels may beused to control propellant casting as is known in the art.

Additional manufacturing systems and methods related to those describedherein are described in Lewis et al., “Digital MicroPropulsion”, Sensorsand Actuators A. Physical, 2000, 80(2) pp 143-154, which is herebyincorporated by reference as if fully set forth herein.

Various additional features may be included, such as electrical pins,connectors, housings, electrode structures, and the like. It will beappreciated that one may use a chamber die having a two-dimensionalarray of propellant chambers and stacking or layering grain elements asdescribed herein to form a three-dimensional thruster array.Additionally, various other processing techniques may be used and theprocessing techniques described may be carried out in other orders or inparallel.

FIGS. 7A and 7B illustrate cross-sectional side and top views,respectively, of exemplary thruster stack array 600 after the additionof propellant 602 and common core regions 604 have been formed. Thecommon core regions 604 are used to channel combustion gases and heatfrom each of the vertically aligned grain elements, one of which isidentified in FIG. 7A (defined generally by chambers 615 of die layers614 a-614 d). Thus, in this example, thruster stack array 600 includesthree vertical stacks of grain elements having a common core region 604and a common exhaust port 603. The common core region 604 and exhaustport 603 may be formed after the propellant is disposed in the structureby drilling, etching, milled, laser milled, or other suitable materialremoval processes. The stack may further include appropriate pin-outsfor electrically connecting the electrodes dies 610, 611, and 612, andfurther include a housing 618.

Thus, thruster stack array 600 includes 12 individual grain elements(defined generally by propellant 602 within each chamber 615 of chamberdies 614 a-614 d), and which may be selectively ignited by appropriatelyaddressing the connections between electrode dies 610, 611, and 612. Thecombustion heat and gasses from combusting any one grain element ischanneled through center core regions 604 and out exhaust ports 603(without igniting or damaging neighboring grain elements).

In some examples, the propellant grain elements may be single castand/or cast together and stacked, and combined into arrays using avariety of laminating methods with adhesives, epoxies, diffusionbonding, or the like. In one example, the stacked grain elements may bein direct contact with one another, but still ignited individuallyand/or in combination without igniting adjacent grains. In otherexamples, the grain elements may be separated by the electrodes orinsulation layers.

FIGS. 8A and 8B illustrate cross-sectional side and top views,respectively, of another exemplary thruster stack array 800 allowingindividual control of a plurality of grain elements. Thruster stackarray 800 is similar to that of thruster stack array 600 illustrated inFIGS. 6, 7A, and 7B, but utilizes two core-burner thruster stackstructures as well as a coaxial thruster structure (similar to thatshown and described with respect to FIGS. 2A and 2B). In other examples,a structure could further include a spiral coaxial thruster similar tothat shown in FIGS. 3A and 3B.

The coaxial thruster includes a coaxial rod electrode 823 and acylindrical electrode 822 encasing propellant 802. Electrodes 822 and/or823 may be coated with burn away insulating coatings to promotecombustion along the open end 825 (similar to that described withrespect to FIGS. 5A-5C). The central rod electrode 823 may also beformed into higher surface area geometries having cross-sectional shapessuch as crosses or star patterns.

In one example, which may be manufactured similar to that of describedfor FIG. 6, the coaxial assemblage uses a central electrode 823 andsegmented cylindrical/ring outer electrodes disposed with insulator dies814 a-814 d between electrodes 810, 811, and 812 and propellant grains.Insulating dies 814 a-814 d may further provide an outer case forelectrical contact feeds to an electrical control unit (not shown).Other combinations of multiple core burning grains and coaxial grains asillustrated in FIGS. 1-7B are possible and contemplated.

The above detailed description is provided to illustrate exemplaryembodiments and is not intended to be limiting. It will be apparent tothose skilled in the art that numerous modifications and variationswithin the scope of the present invention are possible. For example,various examples described herein may be used alone or in combinationwith other systems and methods, and may be modified for varyingapplications and design considerations. Accordingly, the presentinvention is defined by the appended claims and should not be limited bythe description herein.

1. A thruster assembly, comprising: a volume of electrically ignitablepropellant, wherein the electrically ignitable propellant is ignitablein response to the application of electrical power there through; a pairof electrodes operable to ignite the propellant via application ofelectrical power there through; and an insulation layer disposed on atleast one of the electrodes and operable to combust with the propellant.2. The assembly of claim 1, wherein the volume of electrically ignitablepropellant includes a cylindrical ring of propellant defining a coreregion, the core region operable to channel exhaust gasses from theassembly during combustion.
 3. The assembly of claim 1, wherein thevolume of electrically ignitable propellant includes a cylindrical ringof propellant, and the pair of electrodes are disposed on axial ends ofthe cylindrical ring of propellant.
 4. The assembly of claim 1, whereinthe volume of electrically ignitable propellant includes a cylindricalring of propellant, and the pair of electrodes are disposed axiallywithin the propellant.
 5. The assembly of claim 1, wherein the pair ofelectrodes includes coaxially disposed electrodes.
 6. The assembly ofclaim 1, wherein the pair of electrodes are disposed on opposingsurfaces of the propellant and spiraled in a cylindrical structure. 7.The assembly of claim 1, further including an insulating housingsupporting at least a portion of the propellant and the pair ofelectrodes.
 8. The assembly of claim 1, wherein the electricallyignitable propellant is operable to be ignited by the application ofelectrical power through the electrically ignitable propellant.
 9. Theassembly of claim 1, wherein the electrically ignitable propellantincludes a solid electrically ignitable propellant.
 10. The assembly ofclaim 1, wherein the insulation layer is operable to completely combustwith the propellant.
 11. The assembly of claim 1, wherein the insulationlayer is operable to combust with the propellant and expose at least aportion of the electrode.